1. Field of the Invention
The invention relates to a valve means comprising a valve housing, in which an inlet duct for pressure fluid extends, said duct opening into a valve chamber, in which a valve member is urged by spring means in a closed position engaging a valve seat, the valve member opening at a predetermined opening pressure of the pressure fluid present so that pressure fluid arrives by way of an opening cross section at a fluid outlet and flows out from it.
2. Brief Description of the Related Art
Valve means are also termed relief valves and have long been used. For example such a relief valve is disclosed in the British patent publication GB 1 477 238 having an inlet connected with a first pressure chamber. The pressure chamber is closed by a valve member held in its closed position by spring means engaging a valve seat. If an opening pressure is reached, the valve member is lifted from its seat so that the first pressure chamber is connected with an outlet chamber whence the fluid under pressure may flow out.
The U.S. Pat. No. 5,050,637 also shows such a relief valve.
Relief valves are provided for systems to let off fluid medium when the operating pressure exceeds the permissible level and the medium is discharged by the valve opening to lower the pressure. In addition the rapid opening with a sufficient opening cross section for a sufficiently rapid fall in pressure the act of closing the relief valve is important. In the case of conventional relief valves the closing characteristic can not be altered so that the relief valve has the disadvantage of closing relatively late, something entailing an undesired pressure drop in the system. Late closure of the relief valve is more especially entailed when the valve member is opened the pressure fluid acts at a larger area than is the case with the valve member closed with the consequence that a hold pressure, which is below the opening pressure, is sufficient to keep the valve member in its open position. It is only when this hold pressure is no longer reached that the valve closes again.